Nitrogen and phosphorus substitution driven optical anisotropy in bismuth chalcogenides [formula omitted] (X=Bi, N, P; Y=S, Se) from visible to IR region

Abstract

In this study, we present structural, electronic and optical properties of bare and nitrogen, phosphorus substituted orthorhombic bismuth chalcogenide XBi7Y12 (X = Bi, N, P; Y=S, Se) within the framework of Density Functional Theory (DFT). The energy released during the formation of XBi7Y12 shows the favourability of the substitution. The substituted systems showed a systematic tunability of the energy band gap in the IR region. We predicted PBi7Se12 new direct band gap semiconductor having energy gap of 0.30 eV. The effective mass analysis studies were used to identify the type of newly designed semiconductor. The obtained results revealed that carrier effective mass for hole are lower than electron effective masses indicating the expected p-type conductivity in substituted systems. Appearance of a new energy peak near 0.88 eV in the imaginary part of dielectric function makes NBi7Y12 optically active in the IR region which extends their application over a wide spectral range. The optical response of the bare and substituted systems showed light polarization dependence in the IR and visible region indicating their potential towards photo-diodes, photo-catalysis, and photo-detectors.